It's pretty obvious what you're looking at (pause for a moment: because seriously, isn't it AMAZING how penile structures keep such a similar form even in distantly related species? I mean, I realize there's only so many forms that will work for internal fertilization, but it's really stunning how a single efficient form just completely dominates. Natural selection. In your pants).

Anyway, it's pretty obvious what you're looking at. There's some changes in shape, but overall, that's definitely a penis. But there's more to sperm delivery than overall shape. For example, the penis of the alligator isn't hanging out there all the time. It has to emerge. From this:

What you're looking at here is the cloaca of a male crocodilian (see the foot at the bottom? Not particularly great science illustration here, but I suppose they were on a budget). During mating, the penis comes OUT of the cloaca, and the sperm flows along it into the cloaca of the female (fun crocodilian fact: female alligators and crocodiles have a clitoris!).

So we know the sperm gets into the female, and we know the penis everts out of the cloaca, but HOW? The authors of the first paper listed were interested in figuring out exactly how the alligator penis works. So they took four alligator penises, and dissected them very carefully, with care for things like glands and cell types, to determine how exactly the crocodiliants get it up.

And it turns out that it's a weird hybrid of methods. First off, as the authors note:

Phallus stiffness can be achieved in various ways,

(Oh, we've all been there)

The two most common ways are via fibrous tissue, such as cartilage or ligaments, and via an inflatable area of the penis, which fills with blood (or lymph) to create stiff member. And as it turns out, the alligator has BOTH. They have fibrous bodies at the base of the penis, while there is a blood sinus (empty area) at the tip. When the alligator gets goin', the authors hypothesize that the muscles around the base of the panis wcontrol the fibrous bundles to exude the penis from the cloaca. Meanwhile the tip fills with blood to create a rigid structure.

The second question is one of flow. As in, seminal flow. How and where does the sperm flow from the penis to the female cloaca? As you can see from the diagram above, the seminal duct doesn't delivery directly to the penis, it's a little above. So there are two possibilities. The sperm could flow along a groove in the penis into the female cloaca, as occurs in birds like ducks, or it could go through a tube in the penis, as it occurs in mammals.

And here again, it's something of BOTH. The alligator penis does have a groove at the base of the penis.

But the groove (or sulcus) is lined with MORE of the erectile tissue that fills with blood. The authors hypothesize that during an erection, the groove actually closes to form a tube, down which the sperm will flow. There are even muscles that could contract to help it along.

There are even more interesting things about the alligator penis. For example, there are glands associated which might produce a semen like substance, which wasn't thought to exist in alligators. There are also a lot of mucus glands and a great deal of immune cells in the penis, which is probably a good idea if you're hiding it in the cloaca (where all waste products also exit), and then sticking it in someone ELSE'S cloaca where all THEIR waste products exit.

But overall what interests me is how much of a hybrid this penis is. It doesn't just have fibrous tissue or just fluid filled tissue, it has both! It doesn't have sperm flow along a groove or down a tube, it has a hybrid of the two. The wonders of the alligator penis. Not to mention the potential for poetry.

Alligator stiffy, alligator stiffy,
It turns out the way it works it really pretty spiffy!
It's got fibrous tissue, grooves and tubes, to move sperm in a jiffy
So don't underestimate the alligator stiffy!

I can keep going...

Alligator shlong, alligator shlong,
If you feed some to me, I doubt I will live long.
Take away the gator dick, that dinner is just wrong,
Don't you dare serve me that alligator shlong.

Ok, it's not THAT bad.

Alligator willy, alligator willy,
If we keep on with these poems they'll just keep getting silly.
I can handle all the puns, they aren't so awful really,
But don't keep on with the alligator willy.

[...] bits to the common person, and fascinating adaptations to the scientist; e.g., duck penises, alligator penises… I’ll never forget the time my invertebrate zoology teacher showed a video of barnacle [...]

[...] was the most rewarding; especially about the sex of the gator and this article about the alligator penis in the freezer! Guess I would rather freeze with a camera shot then the clinical way. And yes, Gator’s RISE [...]

thx so much for this m8 i couldnt find anything on the reproductive parts and functions of a crocodile for my oral and i thought i was just going to have to fail and get an E but thanks to you im gonna pass